This invention relates generally to indicating devices for indicating a change in a predetermined parameter, and more particularly to heat sensitive indicators for indicating, in a charging operation, that a secondary cell, or battery of secondary cells, has reached full charge.
After full charge is achieved and charging continues beyond the full charge point, it has been observed that in certain cells there results a rise in temperature of the fully-charged battery or cell. In the present invention, this rise in temperature is employed to provide the desired full charge indication by virtue of a relative change in a perceivable parameter of the heat sensitive indicator.
Thus, the indicator according to the present invention is operable with secondary cells, notably sealed cells, which become heated when, after being fully charged, they are subjected to further charging current. Therefore, as used hereinafter, the term "cell or battery" shall refer to sealed cells or like cells which are so heated.
Indicating devices for indicating that a battery or cell has reached full charge in a charging operation are highly useful, since without such indicators it is often difficult to ascertain in simple fashion whether and when a battery or cell has reached full charge. This is particularly true of nickel-cadmium cells because there is no ready way to determine state-of-charge such as, for example, by measuring open circuit voltage as can be used for measuring the charge in lead-acid cells. Therefore, it may be necessary to test or measure the cell charge to ensure that full charge has been achieved. Thus, without the indicating device of the present invention, much effort and electrical energy may be wasted either in measuring the actual charge level of the battery, or in permitting the battery or cell to remain in the charging operation for a time longer than the minimum necessary to fully charge that particular cell.
Accordingly, it is an object of this invention to provide an indicating device for indicating that a cell or battery thereof has reached full charge in a charging operation.
It is also an object of this invention to provide an indicating device for indicating which rechargeable cells have reached full charge in a battery charger.
It is a further object of this invention to provide an indicating device which is relatively lightweight, easily readable, and relatively inexpensive to manufacture.
It is a still further object of this invention to provide an indicating device which may be affixed either to the battery or cell itself, or may be attached to other structures.
Objects and advantages of the invention are set forth in part above and in part below. In addition, these and other objects and advantages of the invention will become apparent herefrom or may be appreciated by practice with the invention, the same being realized and attained by the instrumentalities, combinations, and methodologies pointed out in the appended claims. Accordingly, the invention resides in the novel parts, arrangements, combinations, steps, methods, and improvements herein shown and described.